U.S. Pat. No. 3,116,481 issued to W. Kalin and R. A. Spencer on Dec. 31, 1963 discloses a polarized ringer of the type used in telephone sets. The ringer includes an armature, one end of which extends between overlapping inner and outer poles of a generally rectangular pole piece. The armature is rotatively mounted on a pivot pin and is moved between the inner and outer poles responsive to magnetic flux generated by the application of a ringing signal to a coil associated with the pole piece. This movement results in a clapper that is mounted on the armature striking an adjacent gong.
The pivot pin about which the armature rotates is offset with respect to the polar axis of a permanent magnet that is positioned between the pivot pin and a portion of the pole piece. A magnetic torque is thereby provided that biases the first end of the armature toward the outer pole. This magnetic bias serves to move the first end of the armature to the outer pole when ringing voltage ceases.
This is important for two reasons. First, when the telephone set with which the ringer is associated is connected to a multiple party telephone line and includes a gas tube in series with the ringer, the ringing signal consists of an ac signal superimposed on a dc bias. The ac signal is rectified by the gas tube to provide dc pulses, and the polarity of the pulses is such as to generate a magnetic field that moves the armature toward the inner pole. Therefore, if the armature when at rest is already positioned at the inner pole, no ringing occurs.
The second reason for having the armature return to the outer pole when ringing voltage ceases is that transient signals are generated when the hookswitch or the rotary dial of the telephone set are operated, and the polarity of these transient signals is such as to move the armature toward the outer pole. Therefore, if the armature when at rest is positioned at the inner pole, bell tap may occur as a result of these transient signals. Most telephone users consider bell tap to be an annoyance.
The magnetic bias that returns the armature to the outer pole when ringing voltage ceases cannot, however, be so strong that the ringing signal on long telephone loops is insufficient to move the armature from the outer pole. Therefore the magnetic bias is such as to be insufficient to move the armature to the outer pole if the armature is in direct engagement with the inner pole at the time ringing voltage ceased.
In the embodiment disclosed in the above-noted W. Kalin et al. patent, this sticking of the armature to the inner pole is avoided by riveting a nonmagnetic spacer to the first end of the armature on the side facing the inner pole. The thickness of the spacer is such that the armature is always spaced far enough from the inner pole so that the bias of the permanent magnet is able to return the armature to the outer pole. This arrangement, however, reduces the travel of the armature, and since the velocity of the armature and thereby the energy imparted to the gong by the clapper carried by the armature is proportional to the travel, the acoustic output of the ringer is reduced.
The solution to this problem as disclosed in the prior art is to attach a nonmagnetic cantilever spring member to the armature in place of the spacer. The spring member is deflected as the armature moves toward the pole, and the spring bias combines with the magnetic bias to return the armature to the outer pole when ringing voltage ceases. The armature can therefore be permitted to move into closer proximity with the inner pole.
This arrangement, however, suffers from several deficiencies. First, with the spring member mounted on the armature, both elements must be moved. This increase in mass that must be moved reduces the velocity of the armature over what it would be without the spring member attached. Since the acoustic output of the ringer is proportional to the velocity of the armature at the time of clapper impact, the acoustic output is accordingly reduced. Second, in the prior art ringers, the spring member is either formed, riveted, or staked in place. This operation adds to the cost of manufacture of the ringer. Finally, in all but one prior art ringer, the spring member needs to be adjusted to provide the necessary spring force. This operation also adds to the cost of manufacture of the ringer.